Graphite pellets

ABSTRACT

Air or gas ground graphite is formed into pellets by mixing with finely divided alumina, forming into a paste and then granulating or extruding. The pellets so formed can be used as air or gas ground graphite but with the advantage that the pellets can be in the form of a fixed bed. A typical application is a polishing treatment for lubricating oils to remove aromatics, heterocyclics, sulphur compounds and coloured materials.

finite States Patent Cracknell et a1.

[ Dec. 17, 1974 GRAPHITE PELLETS Inventors: John Roland Cracknell, Esher;

Aleksander Jerzy Groszek, London, both of England The British Petroleum Company Limited, London, England Filed: June 5, 1973 Appl. No.: 367,153

Related U.S. Application Data Division of Ser. No. 98,029, Dec. 14, 1970.

Assignee:

U.S. Cl 208/307, 260/674 SA, 208/310, 208/254, 208/250 Int. Cl ClOg 43/04 Field of Search 208/213, 310, 250, 307, 208/26, 254; 260/676, 674 SA, 668

References Cited UNITED STATES PATENTS 8/1967 Groszek 208/26 3,365,859 l/l968 Sandberg 308/310 3,513,089 5/1970 Geach et al.. 208/310 3,769,199 10/1973 Groszek 208/28 Primary Examiner-Delbert E. Gantz Assistant Examiner-luanita M. Nelson Attorney, Agent, or Firm-Morgan, Finnegan, Durham & Pine 5 7 ABSTRACT 8 Claims, No Drawings GRAPHITE PELLETS This is a division of application Ser. No. 98,029, filed Dec. 14, 1970.

This invention relates to pellets of a carbon product having a large surface and the use of the pellets in the separation of hydrocarbons.

Finely ground graphites prepared by grinding in vacuum or in a gas, e.g., air are well known, and in this specification are termed vacuum ground or gasground grahites." It is also known that finely ground graphites have selective absorption properties, e.g., British Pat. No. l,l26,482 discloses a method of separating long-chain normal hydrocarbons having at least carbon atoms per molecule from their mixtures with other hydrocarbons by contacting the mixture with graphite having a surface area of at least 50m /gm, to absorb selectively the normal hydrocarbons.

However gas or vacuum ground graphites suffer from the disadvantage that finely ground graphite can only be used in the form of a slurry.

lt has now been found that the graphite can be formed into pellets by compounding witha binder. The pellets can be used in the form ofa fixed bed and have the further advantage in that a counter-current process can be used.

Thus according to the present invention there is provided a composition of matter comprising graphite in the form of pellets with a binder comprising finely divided alumina said graphite being a vacuum or gas ground graphite having a surface area of 50 to 2,000 m /gm (BET).

By the term finely-divided alumina" we mean alumina having a surface area in the range 1 to 1,000 m lgm.

The term alumina" is intended to embrace both hydrated alumina and anhydrous alumina.

Preferably the alumina has a surface area in the range 100 to 600 m /gm.

The finely divided alumina is preferably (i) a colloidal alumina manufactured by Du Pont and sold under the name Baymal and having a surface area of 350 m /gm, this material is a microcrystalline fibrous boehmite and is a-alumina monohydrate or (ii) a colloidal alumina manufactured by Laporte and described as Dispersible alumina and designated RD 12026. The preparation of the Baymal alumina is described in U.S. Pat. No. 2,915,475.

The U.S. Pat. No. 2,915,475 discloses the preparation of fibrous Boehmite (oz-alumina monohydrate) and describes the alumina as being in the form of small fibrils (the word fibril meaning an individual crystalline particle) in the shape of laths, at least two of the dimensions of which are in the colloidal range. The laths have their two smaller dimensions in the range 3 to namometers whilst their axial ratio, their ratio between their length and smaller dimensions, falls in the range 50:] to 150:]. Baymal which has a surface area ofabout 350 m /gm would have fibrils having their small dimensions at about 4 nanometers and lengths of between 200 and 600 nanometers. Depending on the conditions of manufacture the fibrils may agglomerate to give thread like aggregates called fibres which may show only partial colloidal properties.

The pellets may contain from 5 to 50% by weight of alumina binder preferably 15 to 40% wt., and from 95 to 50% by weight of graphite, preferably to 60% wt.

According to another aspect of the present invention there is provided a process for the preparation of graphite-containing pellets which process comprises intimately mixing a vacuum or gasground graphite powder having a surface area of 50 to 2,000 m /gm with a finely divided alumina binder, working the mixture into a paste with a suitable liquid and granulating or extruding through a die.

The graphite and the alumina can be mixed either wet or dry. In dry mixing satisfactory results have been obtained by ball milling but high speed mixing in, e.g., a Universal High Speed mixer Type TLEHK 8 made by Gunter Papenmeier A. G. is preferred. ln wet mixing it is preferred to mix using a High Speed Mixer or a colloid mill eg a colloid mill made by Premier Colloid Mills Ltd. using a gap of l.0l6 X l0 "m between the stones. The granulation can be effected by spreading the paste out on a tray, allowing to dry and breaking up the cake so formed.

After extrusion or granulation the extrudate or granules are preferably dried, broken up and sintered in nitrogen for 24 hours at 400C.

The extruded pellets thus prepared are mechanically strong and stable in hydrocarbon solvents such as toluene, 11 -heptane and iso-octane.

The graphite used to prepare the pellets is preferably ground graphite prepared by ball milling graphite in vacuum or a gas, e.g., air.

The grinding of the graphite gives small particles with a plate like graphite structure. Most of the surface area is contributed by the basal planes of the plates, but there is also a significant contribution made by the edges. For air ground graphite the ratio of basal plane surface area to edge surface area in a typical instance is about 4.5:].

As previously described the graphites thus produced have the capability of absorbing normal hydrocarbons on the basal plane surface area and polar compounds, e.g., aromatics, sulphur and nitrogen compounds on the edge surface area. By adjustment of the feedstock and process conditions as described hereunder, the selectivity for either type of compound can be varied.

Thus according to another aspect of the present invention a process for the separation of normal hydrocarbons and/or polar compounds from their mixtures with other hydrocarbons comprises contacting the mixture with graphite pellets as hereinbefore defined to selectively adsorb said normal hydrocarbons and/or polar compounds.

The graphites before compounding with the binder preferably have a surface area of at least 50 square metres per gram and more preferably have a surface area of at least 300 square metres per gram.

The feed mixture for the process may be a petroleum distillate or residue boiling above 30C, particularly a fraction in the waxy distillate boiling range, i.e., 300 to 700C or a waxy raffinate or a dewaxed raffinate. The feed may be a straight run fraction or a waxy raffinate obtained after a selective solvent treatment with, e.g., furfural to remove aromatics. The feed may also be a solvent treated dewaxed lubricating oil fraction or bydrocracked gas oil the treatment in this case being a finishing treatment to improve colour and oxidation stability.

The process can also be used for removing polynuclear aromatic compounds, e.g., 3,4, benzo pyrene from lubricating oils and waxy distillates.

The absorption and desorption stages of the process of the invention are preferably carried out in the presence of liquids in which the adsorbed and subsequently desorbed components are soluble. These liquids may be the same or different. Thus, the liquid may comprise a single paraffin hydrocarbon, such as n -heptane or iso-octane, or it may comprise a mixture of hydrocarbons including refinery streams such as Primary Flash Distillate or an aromatic or alcoholic solvent may be used. The solvent used for dewaxing is preferably a polar solvent since such solvent promotes the absorption of non-polar compounds, such as waxes, including long chain n-paraffins. For the removal of polar compounds, the preferred solvent is a n-paraffin.

The adsorption stage of the process of the invention may be performed at a temperature of from -50C to 200C. if a mixture of paraffms, aromatics or alcohols is used its boiling range should be within this range. Hydrocarbons whose atmospheric boiling point is outside this range may be used at sufficient pressure to achieve a boiling point within the range quoted, provided that the desorption temperature is not above the critical temperature. Thus, for example, liquified propane and butane (L.P.G.) may be used under certain conditions.

For processing waxy raffmates and distillates a solvent is preferred. For a mobile liquid feedstock such as gas oil or kerosene no solvent is required.

The loading of the graphite with the absorbed components will depend on the nature of the feed, but should desirably be as low as possible. The loading expressed as graphite:feed ratio by wt is preferably less than 1:2, and more preferably less than 1:1 wt. The ratio of absorbed components to graphite may, however, be as low as 1:100. When refining waxy raftinates or distillates with dewaxing as the prime objective the overall graphite:feed ratios usually be in the range 1:1 to :1. If a multistage batch treatment is being used the individual stage graphite:feed ratios may be in the range 0.5:1 to 4:].

When applying a polishing treatment to a dewaxed raffinate with the object of removing aromatics, heterocyclics, sulphur compounds and coloured materials, the overall graphite:feed ratios may be in the range 0.511 to 4:1

The feed solvent/feed ratios can vary from 0:1 and 50:1 by wt. Suitable contact times between the graphite and the feed may be from 1 minute to 24 hours. The adsorption of n-paraffms is promoted by low temperatures within the stated range, and the preferential adsorption of aromatics by higher temperatures. Thus, the temperature should not be above 100C and preferably from 0 to 50C if it is desired to adsorb paraffins. The temperature may be above 30C, and preferably from 50 to 200C where aromatics are to be adsorbed.

The adsorbed hydrocarbons may be recovered from the graphite by contacting it with a liquid which may be the same as that of the adsorption stage, or a chemically identical or different liquid may be used. The use of the same solvent is preferred.

The temperature may be in the range from room temperature up to 1,000C and pressure may be applied to keep the material treated in the liquid phase.

Typically the temperature of desorption is in the range of 400C.

Alternatively, certain feedstocks can be treated over the graphite alumina adsorbent in the gas phase.

The pressure at which desorption is carried out should be such as to maintain the eluting material in the liquid state and will accordingly be within the range 10 to 3,000 psig. It will of course be determined by the vapour pressure of the eluting material at the desorption temperature. The contact time will be within the range 1 to minutes. The solvent desorbate ratio is preferably from 11:1 to 100:1.

The method is desirably carried out in a cyclic type of operation, for example, by percolating the feed mixture together with liquid through a bed of graphite pellets, removing non-adsorbed feed material and liquid from the bed, stripping the liquid from the nonadsorbed feed material, desorbing the adsorbed material from the graphite with the liquid, removing the desorbed material and liquid from the bed, stripping liquid from the desorbed material, and re-contacting the graphite with the feed mixture. In such a fixed bed type of operation reaction conditions, in particular liquid flow rate, should be chosen so that the pressure drop across the bed is not excessive.

In the case of preparation of lubricating oil basestocks, the feedstock may be treated by any number of adsorption/desorption cycles to give a desired pourpoint and viscosity index. The pour point of the treated material will decrease as the extent of removal of adsorbed materials increases, but the yield will also decrease. Waxy raffinate fractions treated by the process of the invention have in general higher viscosity indexes, lower cloud and pour points and lower sulphur contents than fractions obtained by conventionally treating similar feedstocks. They also have better response to oxidation inhibitors. in addition to the oil products obtained, the adsorbed and subsequently desorbed material, i.e., normal paraffins and/or aromatics may be of use, particularly if it is waxy paraffmic or aromatic hydrocarbon material.

The invention is illustrated by the following examples.

EXAMPLE 1 A Kuwait waxy distillate having a pour point of 38C 38C 220 centistokes 60C 64.34 do. 77C 3157 do. 99C 1509 do.

viscosity index 67 viscosity at sulphur 3.18% wt was mixed with the pelletted graphite and isooctane under the following conditions:

Loading by wt 5:1 (pelletszdistillate) Solvent iso-octane at 20 ml per g feedstock Temperature ambient Contact time 24 Hr.

Viscosity at 38C 164.52 c St (220) Viscosity index 80 (67) Four point (micro) +4C (+38C) Figures in brackets refer to the original distillate.

EXAMPLE 2 A finished Kuwait/l meg lubricating oil having a viscosity of 1 l0 contistokes at 100F and a viscosity index of 95 determined in accordance with ASTM D 2270 was percolated through a bed of 14-100 BSS graphite alumina crushed extrudate under the following conditions:

Solvent Temperature Space velocity wt of adsorbent iso-octane at 3 ml per g feedstock ambient 0.365 vol/vol/hour contact time 2.74 hours 977 g length of bed 45 cms.

The graphite alumina adsorbent was prepared by mixing 3 parts by weight of graphite obtained from Solid Lubricants Limited and prepared by grinding in air in a cascade ball mill to a surface area of 375 m /gm (BET) with 1 part of Baymal alumina and then ball milling the dry solids for minutes. The mixture was then worked into a thick paste and extruded through a 3.175 X 10"M die. The extrudate was dried in air, sintered in nitrogen at 400C for 24 h and crushed and sieved to yield 14-100 mesh BSS adsorbent.

The treated oil was collected in 9 fractions having the properties shown in Table 1.

The results show that treatment with the graphite pellets improves the colour stability of the lubricating oil and removes aromatics, sulphur and nitrogen compounds.

Overall Yield of unadsorbed oil 97% Overall graphite:feed oil ratio 0.082:l

After passing the oil, the column was washed with iso-octane at 250C and 274 g of waxes and aromatics recovered. After the desorption the feedstock was percolated again and 2 fractions collected comprising a total of 1,855 g as shown in Table 2.

Table 2 Second Run Oil to Fraction Cumulative Graphite ASTM 8% Nppm C No. wtg Ratio Colour EXAMPLE 3 EXTRACTION OF POLYNUCLEAR COM- POUNDS BY GRAPHITE/ALUMINA The pellets were prepared exactly as in Example 2 but alumina manufactured by Laporte having a surface area of 2m /gm was used in place of Baymal Alumina. The pellets were the same size as in Example 2 viz 4-l00 mesh B.S.S.

3.4- Benzo yrene U g X Oil (a) A middle East waxy distillate. The procedure of Example 2 was repeated but, 5 parts by wei t of oil treate with 1 part of gra hite/ alumina at 5 C withsolvent Feed oil As in (a) above, 5 parts of oil treated with 1 part of graphite/alumina at 50C without solvent As above, 1:1 treatment with gra hite/ alumina at 20 in isoctane SAE 10 lubricating oil prepared by hydrogenation of a Kuwait vacuum distillate As in (a) and (b) above 5 parts of oil treated with 1 part of raphite [alumina at 50 no solvent X determined by liquid chromatography and UV spectroscopy. determined by FDA 121.2589 (c).

The oil used in Example 3 (a) has the following inspection data:

The oil used in Example 3 (a) had the following inspection data:

Kinematic viscosity at 100F 20.5 centistokes 140F 9.6 do. 2l0F 3.86 do.

Specific Gravity /60 0.901

60 The oil used in Example 3 (b) gave the following Vacuum Engler distillation data.

lnitial listing point 343 5 10% distilled 383 Final listing point 472 Kinematic viscosity at F 20.5 centistokes Cominued was filled with 300 grams of 6-25 858 mesh crushed graphite/alumina extrudate. 210F 3.86 do. A solution of 56.25 grams of the waxy Raffmate of speclfic Gravity 60/60 Kuwait origin in 500 millitres of isooctane was pumped through the column at aflow rate of 200 mls per hour and a residence time time of 2 hours. The removal of EXAMPLE 4 fractions of the unadsorbed oil was effected by pump- GRAPHITE TREATMENT OF A HYDRO- ing isooctane through the Column. Equal volumes of CRACKED (3A5 01L solution issuing from the Column gave the following The pellets were prepared exactly as described in Exyields and P Points w the Oil was isolated- The ample 3 and the hydrocracked gas oil, boiling range temperature of the ehmoh was 225C 370C, was percolated through graphite/alumina pellets without solvent at room tempera- TABLE I1 ture, the products being collected at oil to graphite ratics of 20 and 35 1 Absorbent Graphite (75%) Pechiney GB 300 alumina (25%) 625 E55 The percolated oils have been found to be much lighmesh' ter in colour and had a significantly greater stability to Weigh Ems Eluent isooctanc light and heat compared with the feedstock as shown Flow mm C 200 mls/hr i h table b Residence Time in olumn 2 hours Char e Oil Kuwait Waxy These results show that I polishing of gas 0115 by per- Rafinme colation through graphite/alumina absorbents "1- Charge Weight 56.2 5 grams creases substantially their stabilities to light and heat. wr fg g i i g M Ministry of Defence test. Products.

EXAMPLE 5 Eluted with isooctane Preparation of Graphite/Alumina absorbent ggli zf f g- The graphite, 75 grams, was mixed in a dry state with Fr t 2 Weight percent 23,5

Pour point F +5 25 grams of the alumina, which has a disperstble type Fraction 3 weight percent 7.2 GB 300 obtained from Pechmey St Gobam. 3O Pour point "F +35 The graphite had a surface area of 380 m lgm and the g 'i'g m g Percent 8 alumina 300 /gm. Fraction 5 weiglgt percent 5.3 The minimum of water, about grams, was added +55 Fraction 6 weight percent 3.9 gradually with continuous mixing to give a firm smooth p point +5 pasta Fraction 7 weight percent 4.6

. Pour point 60 The paste was extruded through 1/16 inch diameter Fraction dutqd with hm die. The extrudate was allowed to dry slowly overnight nlchlonde 0 Pour point F 100 and then sintered in nitrogen at 400 C.

Percolated Oils Test Feedstock to to Graphite Ratio Graphite Ratio 20:1 35:1

Colour, ASTM 3.5 0.5 0.5 Ex sure to sunlight light brown no de it, no de sit, l ay on window sill deposit oil c ear oil c ear DEF 2060 test, Method 16 (heating at 2l0F for l6 hours) Total sediment, mg/lOOm 0.23 0.1 0.06

The sintered material has the physical properties We claim:

shown in Table 1 below:

TABLE I Graphite/Alumina GB 300 6-25 858 mesh BET Surface Area, m lg 355 Bulk Density Maximum 0.61 gms/cc 0.52 gms/cc Separation of a Waxy Raffinate having a viscosity of l 10 centistokes at l00F and a viscosity index of 95 determined in accordance with ASTM D 2270 over a column of Graphite alumina absorbent. A column 89 centimetres long and 5.7 centimetres square cross section l. A process for the separation of n-paraffins and/or polar compounds selected from the group consisting of aromatics, sulfur and nitrogen compounds from a mixture with other hydrocarbons, which process comprises contacting said mixture with pellets consisting essentially of 50-95% weight of a vacuum or gas ground graphite having a surface area of 502,000 m lgm (BET) and, as a binder, 5-50% weight of a finely divided alumina, to adsorb selectively the nhydrocarbons under a pressure sufficiently high to maintain the mixture in the liquid phase and at a temperature in the range -50200C.

2. A process as claimed in claim 1 wherein the feed is a petroleum fraction boiling in the range 300 to 700C and the process is effected in adsorption and desorption stages.

3. A process as claimed in claim 1 wherein the process is effected in the presence of a liquid in which the adsorbed and subsequently desorbed components are soluble.

4. A process as claimed in claim 3 for the removal of waxes wherein a polar solvent is employed.

5. A process as claimed in claim 3 for the removal of polar compounds wherein a n-paraffin solvent is employed.

6. A process as claimed in claim 1 for the removing aromatics, heterocyclics, sulphur compounds and coloured materials from a dewaxed raffinate wherein the overall graphite feed ratio is in the range 0.5:1 to 4:1.

7. A process as claimed in claim 1 for improving the heat and colour stability of a hydrocracked gas oil or a lubricating oil which process comprises contacting the gas oil or lubricating oil with graphite pellets consisting essentially of 50-95% weight of a vacuum or gas ground graphite having a surface area of 502,000 m /gm (BET) and as a binder, 5 to 50% weight of a finely divided alumina.

8. A process as claimed in claim 1 for removing polynuclear aromatic compounds from lubricating oils and waxy distillates with graphite pellets consisting essentially of 50-95% weight of a vacuum or gas ground graphite having a surface area of 50-2,()00 m /gm (BET) and as a binder, 5 to 50% weight of a finely di 

1. A PROCESS FOR THE SEPARATION OF N-PARAFFINS AND/OR POLAR COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF AROMATICS, SULFUR AND NITROGEN COMPOUNDS FROM A MIXTURE WITH OTHER HYDROCARBONS, WHICH PROCESS COMPRISES CONTACTING SAID MIXTURE WITH PELLETS CONSISTING ESSENTIALLY OF 50-95% WEIGHT OF A VACUUM OR GAS GROUND GRAPHITE HAVING A SURFACE AREA OF 50-2,000 M2/GM (BET) AND, AS A BINDER, 5-50% WEIGHT OF A FINELY DIVIDED ALUMINA, TO ABSORB SELECTIVELY THE NHYDROCARBONS UNDER A PRESSURE SUFFICIENTLY HIGH TO MAINTAIN THE MIXTURE IN THE LIQUID PHASE AND AT A TEMPERATURE IN THE RANGE -50*-200*C.
 2. A process as claimed in claim 1 wherein the feed is a petroleum fraction boiling in the range 300* to 700*C and the process is effected in adsorption and desorption stages.
 3. A process as claimed in claim 1 wherein the process is effected in the presence of a liquid in which the adsorbed and subsequently desorbed components are soluble.
 4. A process as claimed in claim 3 for the removal of waxes wherein a polar solvent is employed.
 5. A process as claimed in claim 3 for the removal of polar compounds wherein a n-paraffin solvent is employed.
 6. A process as claimed in claim 1 for the removing aromatics, heterocyclics, sulphur compounds and coloured materials from a dewaxed raffinate wherein the overall graphite feed ratio is in the range 0.5:1 to 4:1.
 7. A process as claimed in claim 1 for improving the heat and colour stability of a hydrocracked gas oil or a lubricating oil which process comprises contacting the gas oil or lubricating oil with graphite pellets consisting essentially of 50-95% weight of a vacuum or gas ground graphite having a surface area of 50-2,000 m2/gm (BET) and as a binder, 5 to 50% weight of a finely divided alumina.
 8. A process as claimed in claim 1 for removing polynuclear aromatic compounds from lubricating oils and waxy distillates with graphite pellets consisting essentially of 50-95% weight of a vacuum or gas ground graphite having a surface area of 50-2,000 m2/gm (BET) and as a binder, 5 to 50% weight of a finely divided alumina. 